linux-imx

// SPDX-License-Identifier: GPL-2.0

/*

 * Workingset detection

 *

 * Copyright (C) 2013 Red Hat, Inc., Johannes Weiner

 */

​

#include <linux/memcontrol.h>

#include <linux/writeback.h>

#include <linux/shmem_fs.h>

#include <linux/pagemap.h>

#include <linux/atomic.h>

#include <linux/module.h>

#include <linux/swap.h>

#include <linux/dax.h>

#include <linux/fs.h>

#include <linux/mm.h>

​

/*

 *      Double CLOCK lists

 *

 * Per node, two clock lists are maintained for file pages: the

 * inactive and the active list.  Freshly faulted pages start out at

 * the head of the inactive list and page reclaim scans pages from the

 * tail.  Pages that are accessed multiple times on the inactive list

 * are promoted to the active list, to protect them from reclaim,

 * whereas active pages are demoted to the inactive list when the

 * active list grows too big.

 *

 *   fault ------------------------+

 *                                 |

 *              +--------------+   |            +-------------+

 *   reclaim <- |   inactive   | <-+-- demotion |    active   | <--+

 *              +--------------+                +-------------+    |

 *                     |                                           |

 *                     +-------------- promotion ------------------+

 *

 *

 *      Access frequency and refault distance

 *

 * A workload is thrashing when its pages are frequently used but they

 * are evicted from the inactive list every time before another access

 * would have promoted them to the active list.

 *

 * In cases where the average access distance between thrashing pages

 * is bigger than the size of memory there is nothing that can be

 * done - the thrashing set could never fit into memory under any

 * circumstance.

 *

 * However, the average access distance could be bigger than the

 * inactive list, yet smaller than the size of memory.  In this case,

 * the set could fit into memory if it weren't for the currently

 * active pages - which may be used more, hopefully less frequently:

 *

 *      +-memory available to cache-+

 *      |                           |

 *      +-inactive------+-active----+

 *  a b | c d e f g h i | J K L M N |

 *      +---------------+-----------+

 *

 * It is prohibitively expensive to accurately track access frequency

 * of pages.  But a reasonable approximation can be made to measure

 * thrashing on the inactive list, after which refaulting pages can be